Process of chlorinating propane and its partially chlorinated derivatives



DERIVATIVES June 1935- H. B. HASS El AL PROCESS OF CHLORINATING' PROPANEAND ITS PARTIALLY CHLORINATED Filed May 1 Patented June 4, 19 35 UNITEDSTATES PA'II'E It is theobject of trimethylene chlorid NT" OFFICEPROCESS OFCHL ORI NA'I'ING PBOPANE TIALL CHLO ITS ,PAR Y TIVES Henry B.Bass yette, Ind., Foundation, tion of Indiana and Earl T. assiznors toWest Lafayette, Incl, a corpora- RINATED DERIVA- ucnee. West Lara ueResearch Application May 1, 1934, SerialNo. 723,366 22 Clalms. (Cl.260-468) our invention to synthesize e (1,3-dichloropropane) .by

the chlorination of propane.

While various hydrocarbons have been chlorinated, for many years, priorto our work very little has been done in chlorinating propane.

Two-thirds of a century ago, in 1869, Schorlemmer did indeed report thathe chlorinated propane, by the actionof sunlight at room temperature ona gaseous .mixture of bell-jar; but, accord dichloride obtained chlorineand propane in a ing to his report, the only was 1,2-dichloropropane.

(See summar in Chemical Reviews, volume 8,

pages 1 to 80,

' Lowry.)

year .1931, by Egloff, Schaad, and

Indeed, according to a commonly accepted rule for chlorination,

(which rule is shown by our work to be erroneous,) the only dichlorideobtainable by the 1,2-dichloropropane that according to tha obtain1,3-dichloropropane (trimethylene chlochlorination of propane is(propylene dichloride); so t rule it was impossible so to ride). ,Thatcommonly accepted rule is with reference to the halogenation of alkylhalides-for in forming a dichloride of propane by chlorine substitutionit chloride-and of Herzfelder above cited):

is necessaryto form first a monois aptly summariz ed in the words(quoted on page 4 of the summary When in a monohalogen compound, asecond halogen atom is introduced, it always attaches itself to thatcarbon atom which is situated next to the carbon atom already unitedwith halogen."

This supposedly be supported by (ibid. p..29,) in chlo only butylenedichloride" product, and in any many reports.

universal rule has seemed to Thus: Shfiyen, rinati'ng n-butane, reportedas a dichlorination butylene dichloride the two chlorine atoms arenecessarily on adjacent carbon atoms;Butlerow, isobutane, reported(ibid. p. 30,) in chlorinating only 1,2-dichloroisobutane (isobutylenedichloride) as a dichlorination product; and Schorlemmer, as alreadynotedywhen he chlorinated propane only propylene dichl many years ago,reported oride (1,2-dichloropropane) as a dichlorination product. TheSharples Solvents Corporation (Bulletin ,Chemicals Derived from thePentanes) lists only 1,2-dichloropentane, 2,3-dichloropentane, and2,3-dichloroz-methylbutane, as dichlorides produced in the chlorinationof a mixture of n-pentane and iso- .pentane. In all the se nodichlorination is reported in which chlorine is substituted on twonon-adjacent, carbon carbon.

atoms of a parafiin hydro- We have obtained in the chlorination ofpropane, in addition to 1,2-dichloropropane (propylene dichloride), aconsiderable amount of other dichlorides of propane; and have found thatin these additional dichlorides 1,3-dichloropropane (trimethylenechloride) is not only present, contrary to the commonly accepted ruleabove referred to, but is, the one which usually predominates. "We havealso found that by controlling the conditions .we may increase theproportion of 1,3-dichloropropane; by carrying on the chlorinationprocedure wholly at high temperature, m the manner which has alreadybeen pointed out generically and in some specific cases in ourco-pending application Serial No. 590,046, filed February 1, 1932, forincreasing the ratio of primary substitution to secondary and/ortertiary substitution. 7

When propane is chlorinated, the variants in the chlorinationvproducts,up to and including dichlorides, are shown bythe following:

CH;OHCI-CH1 H0] (Z-chloropropane) (hydrogen 7 chloride) 1 carom-enact or(Propane) (Chlorine) Hichloropropane) 01 (3)CHzCl-CHr-CHa-I-ClaTCHCIrCHz-CHz-i-HCI (l-chloropropane) or(1,1-dichloropropane) second of the desired 1,3-dichloropropane.However, substantial amounts of 1,3-dichloropropane are obtained even atlow temperatures; so that our process includes not only chlorinationunder optimum conditions for primary-carbon chlorination, with orwithout thermal acceleration, a chlorination of propane under otherconditions. Either photochemical or catalytic acceleration gives goodresults. f

In thermal chlorination atrelatively high temperatures, vwe prefer toheat both the chlorine and the propane or monochloride of propaneseparately to the desired reaction temperature, and to mix them at thattemperature; for which purpose it is desirable, in order to preventflame, that one of the gases be injected into the other at a highvelocity, so that it the speed of flame propagation, and to have suchinjection with a turbulent flowwhich produces an intimate mixing whichenables the ingredients to becomeuniformly dispersed in each otherbefore any considerable amount of chlorination takes place; for thisavoids the formation of undue amounts of highly chlorinated products,which are formed if thereaction 'occ'urs in the presence of a localexcess of chlorine.

In the chlorination process, both polychlorin- I ated products andmonochlorinated products are obtained. By providing sufficient chlorine,at one or more jets, and re-cycling the monochlorides, the proportion ofdichlorides to monochlorides obtained may be increased.

In any of these cases, the chlorination of propane yields chloridesother than the desired 1,3- dichloropropane (trimethylenechloride) Theseother chlorides. whether monochlorides or polychlorides, are desirablysuitably separated from the desired 1,3-dichloropropane, conveniently byrectification. That can readily be done, with the single exception ofone trichloride (1,2,2- trichlcropropane), on account of the fairly widedifferences in the boiling points involved; and the conditions ofchlorination are so controlled that the production of trichlorides andparticularlyof that 1,2,2-trichloride is largely avoided. The desired1,3-dichloropropane (trimethylene chloride) has a boiling point of120-121 C., (the boiling point of 125 C. commonly given in theliterature is erroneous) and the various monochlorides and the otherdichlorides of propane all have boiling points at least 12 away fromthat temperature.

We may separate the l-chloropropane from the 2-chloropropane obtainedaccording to Equation 1, and also from any polychlorides which areproduced at the same time; then recycle the l-chloropropane tochlorinate it in accordance with Equation 8, desirably under conditionswhich yield a maximum amount of l,3-dichloropropane; and then separatethe 1,3-dih1oropropane from other chlorides present.

The essential features of our process are the chlorination of eitherpropane or l-chloropropane, or both, to yield 1,3-dichloropropane; andthe separation of that 1,3-dichloropropane from other chlorides present.

We may carry out our process with various forms of apparatus. Onesuitable form is essen-' tially that of our aforesaid co-pendingapplication Serial No. 590,046. The accompanying drawing shows thatapparatus with some variation.

In that drawing: Fig. l is a diagrammatic view of our preferredapparatus; Fig. 2 is a fragas thermal chlorination, but also, eitherenters in excess of mental diagrammatic view showing a modification ofpart of that apparatus; and Fig. 3 is another fragmental diagrammaticview, showing another modification.

The propane to be chlorinated is supplied by a valved pipe l0 and thechlorine by a valved pipe II. The propane may if desired be diluted byan inert diluent, such as nitrogen, supplied by a pipe 9; but if sothediluent does not enter into the chemical reaction, although it doesexert an effect on physical conditions, as by its capacity to absorbheat. This diluent is often desirable in the chlorination of propane;desirable to get a quick heating of the material to be chlorinated ifsuch material consists wholly of l-chloropropane, in which case thenitrogen supplied may be hot.

The proportions of the propane and the chlorine are desirably controlledto keep the chlorine present below that necessary for an explosivemixture.

but is especially.

The propane-supply pipe Ill and the chlorinesupply pipe H preferablylead to separate vaporizingand/or preheating coils l2 and [3respectively, located in a suitable heating device I4; which isconveniently an'ordinary bath of water or of molten salts accordingto'the temperature desired. Ordinarily the propane and chlorine suppliedare in liquid form, so that vaporization is necessary to get them intothe gaseous phase in which we conduct our process; and desirably wepreheat both the propane and the chlorine additionally in the coils l2and I3, to raise them to a desired reaction temperature before mixingthem. This is desirable to obtain a maximum proportion ofl-chloropropane as a m'onochloropropane, and of 1,3-dichloropropane as adichloropropane; and to obtain these maximum proportions in thermalchlorination the temperature to which the gases are raisedbefore beingmixed should be at least 250 C., and desirably should be in theneighborhood of 500 C. or over. These optimum temperatures are usuallylower than that in photochemical and in catalytic chlorination.

The propane and the chlorine, either or both heated if desired,desirably pass separatelyas gases to a reaction passage l6, where theyare mixed at high velocity and react. The velocity of injection of onegas into the other, as has already been stated, is desirably greaterthan the speed of flame propagation of the chlorination reaction, and isusually of the order of fifty to a hundred miles per minute. Thechlorine supplied is under sufficient pressure to produce this speed.The reaction tube I6 is desirably a crooked one, as is shown-in Figs. 1and 3, to create a turbulence which produces intimate diffusion of thepropane and the chlorine in each other before any considerablechlorination has occurred, so that flame is effectively prevented andthe formation of free carbon lessened and practically avoided. However,especially in photochemical or catalytic chlorination, the reactionpassage may be in the form of a straight tubev I6, as is shown in-Fig.2. The chlorine is injected into the reaction tube 16 or I6 by one ormore jets l5'.--"A'single jet is shown in Figs. 1 and 2; and a pluralityof jets IS in Fig. 3. When there are a plurality of such jets l5, theyare desirably arranged at spaced points along the crocked reaction tubel6, as is clear from Fig. 3, so that the reaction of the chlorineinjected at one jet may be completed or nearly so before the chlorinefrom the next jet is introduced. The

liquids are drawn oif respectively type.

reaction passage, especially if it is a crooked one as is the reactionpassage H5 in Figs. 1 and 3, is desirably immersed ,in a bath |1,Ias of"molten salts, to absorb the heat of the reaction, which is'anexohthermic one; although if the chlorination is photochemical orcatalytic, such bath I! may be omitted as in Fig. 2. Suitable burners I8may be provided for heating. the bath containingthe coils l2 and i3, andfor initially heating the heat-absorbing bath l1.

When the chlorination is to be a photochemical chlorination, suitablelight-giving devices, such as incandescent bulbs is, may beprovidedaround the reaction tube l6 and the reaction tube is made ofsome material, such as silica or glass, which permits the passagethrough its walls of the reaction-accelerating light. rination isto becatalytic, any suitable catalyst 20 may be put in the reaction tube i6.Both photochemical and catalytic acceleration may be used, as is shownin Fig. 2. Various catalysts may be used, such as granular carbon,antimony chloride, stannic chloride, or other known chlorinationcatalysts. -If desired, a plurality of reaction-accelerating expedientsmay be used, such as heat and light, or heat and a catalyst, or lightand a catalyst, or light and heat and a catalyst. In general, thetemperature of the reaction may be lowered if a catalyst or light isused to accelerate the recation.

The reactionproducts, with any recycled unreacted propane, (fordesirably there is an excess of propane so that the formationof'trichlorides and more highly chlorinated products is minimized.) passfrom the reaction tube IE or Iii immediately to the worm 2| of a cooler22; by which they are cooled quickly to a temperature in theneighborhood of room temperature. This immediate cooling lessenspyrolysis.

From the worm 2|, the reaction products pass to the bottom of awater-scrubber 23, of anyconventional form; in which the water takes up;the hydrochloric acid present. This hydrochloric acid, and any condensedorganic vapors, pass out from the bottom of the water-scrubber 23 by apipe 24to a separator 25; whence thehydrochloric acid is drawn off atone level, desirably into a container 26, for sale as a by-product, andthe organic liquids are drawn oif at another level and passed to analkali-scrubber 21. The levels at which the hydrochloric acid and theorganic depends on which has the greater density, for the density of theorganic liquids will depend upon whether monochlorides or polychloridespredominate; and so suitably valved pipes 28 and 29 are provided bywhich either liquid may be drawn off at a lower level and either at ahigher level. Any vapors which rise in the water-scrubber 23 pass offfrom the top thereof through a pipe 30 to an alkali scrubber, 3|. Thealkali scrubbers 2'! and 3| are'provided out of abundant caution toensure the removal of all hydrochloric acid.

Valve pipes 32and 33'from the outlets of the two alkali scrubbers 27 and3| join each other, and lead to a rectifying column 34, of any suitableThe temperatures in this rectifying column 34 are so controlled that thechlorinated hydrocarbons or mixed chlorides are condensed and pass asliquids to the bottom of the column, whence they may be drawn oilthrough a pi. e 35.

The unreacted propane, together with the inert diluent (such asnitrogen) if any is present, passes out at the top of the rectifyingcolumn 34, and is divided in conventional manner by a de- When thechlophlegmator 3B and take-off portions,

' cause its chlorination.

The chlorinated hydrocarbons or mixed chlorides drawn off by the pipe 35may be supplied to a suitable storage receptacle 43 if desired, througha valved outlet 44. However, these chlorinated hydrocarbons are amixture, and it is usually desirable to separate some from others. Tothis end, they may be passed through any desired number of rectifyingcolumns 45, 46, 41, 48, etc., to get any desired separation. Usuallythere will be a plurality of rectifying columnsrfor getting additionalseparations; which may be varied at will. as will be clear from thefollowing table of boiling points:

Monochlon'des 2 Chloropropsne, boils at 34.7 C. 1 Chloropropane, boilsat 46.8 C.

. 2,2-dichloropropane, boils at 67 C.

. 1,1-dichloropropane, boils at 87 C. 1,2dichlor0propane, boils at 96.8"C.

. 1,3-dici1loropropane, boils at l20l21 C.

Convenient ist fractionation Convenient 2d fractionation Convenient 3dfractionation r Trz'chloropropanes rides, without further separation,may pass through a valved pipe 50 to a recycling pipe 5|, provided witha recycling pump 52, for returning the mixed monochlorides to anyconvenient point in the propane-vaporizing-and heating tube l2.

In some cases, however, the mixed monochlorides from the top of therectifying column 45 are led to the rectifying column 46; whichseparates the two monochlorides. The 2-chloropopane passes out from thetop of the rectifying column 46, and may be collected in a receptacle53. The l-chloropropane passes out from the bottom of the rectifyingcolumn 45, by a valved pipe 54 which leads to the recycling pipe 5|. Byclosing the valve in the pipe 50 and opening the valve in the pipe 54,the recycling may be of the l-chloropropane only, without contaminationby the 2- chloropropane which can yield none of the desired1,3-dichloropropane.

It is usually desirable to have a preheating device 63in the pipe 5|,for vaporizing and producing any desired pre-heating of thel-chloropropane.

The mixed polychlorides from the bottom of the'rectifying column 45 maypass to a rectifying column 41, in which a separation may be obtained oneither side (speaking in terms of boiling-point sequence) of the desired1,3-dichloropropane-that is, between e and f or between f and g, asdesired. Conveniently, however, this 4- separation is made between e andI; so that all three dichlorides except 1,3-dichloropropane will passout at the top of the rectifying column 41, to be collected in areceptacle 55, while a mixture of the 1,3-dichloropropane withany'trichlorides passes out at the bottom of the rectifying column 4 1.The amount of the trichlorides maybe kept relatively small by theabove-stated procedure of using a large excess of material to bechlorinated over chlorine, so that only a small proportion ischlorinated at each pass through the reactor. It is of course desirablealso that the dichlorides should be rigorously removed from the materialto be recycled. What trichlorides there are may be substantiallyseparated from the desired 1,3-dichloropropane by the rectifying column48; from which the trichlorides pass out from the bottom into areceptacle 56, while the 1,3-dichloropropane (trimethylene chloride)passes out at the top into a receptacle 51.

For simplification of illustration, the conventional dephlegmators andwier-boxes for separating the vapors which pass oil at the top of arectifying column into reflux and take-oil portions are shown only inconnection with one rectifying column (34), although ordinarily theywould be used on all columns.

We desirably provide fiowmeters 60 in the 'pipes III, II, 39 and 5 I togive information which facilitates the control of the quantities ofreactants supplied.

In operating our process, we usually maintain a constant supply ofpropane by the pipe l0. But that is not necessary; for the chlorinationto get 1,3-dichloropropane may be of l-chloropropane alone. Suchl-chloropropane, obtained from any desired source, may besupplied by wayof a pipe 6| through suitable valves to either pipe 39 or pipe 5!; sothat by opening a valve in either pipe BI and closing the desired valvesin the pipes in and 54, it is possible to operate the system simply tochlorinate l-chloropropane. In that case, the rectifying column 46 wouldnormally be shut off, by closing the valve at its entrance. If unreactedl-chloropropane is to be recycled the valve in the pipe 50 would beopened.

Ordinarily, however, as has already been stated, we prefer to provide aconstant supply of propane, by way of the valved pipe I; so that therewill be simultaneous chlorination both of propane, mainly to themonochloropropanes, and of l-chloropropane, mainly tothedichloropropanes,

in the reaction tube.

We claim as our invention:- l. The process of producing trimethylenechloride, which consists in subjecting a gas of the class consisting ofpropane and l-chloropropane to a. chlorination reaction with gaseouschlorine to yield trimethylene chloride and other chlorides of propane,and separating the trimethylene chloride from other chlorides.

2. The process of producing trimethylene chloride, which consists inchlorinating gaseous propane with gaseous chlorine to obtain a mixtureof trimethylene chloride and other chlorides of propane, and separatingthe trimethylene chloride from other chlorides.

3. The process of producing trimethylene chloride, which consists inchlorinating gaseous lchloropropane with gaseous chlorine to obtain amixture of trimethylene chloride and other chlorides of propane, andseparating the trimethylene chloride from other chlorides. I

4. The process of producing trimethylene chloride, which consists insubjecting .a gas of the class consisting of propane and l-chloropropaneto a chlorination reaction with gaseous chlorine under thermalconditions which accelerate the reaction, to yield trimethylene chlorideand other chlorides of propane, and separating the trimethylene chloridefrom other chlorides.

The process of producing trimethylene chloride, which consists inchlorinating gaseous pro- .pane with gaseous chlorine to yieldmonochlorides and polychlorides, separating l-chloropropane from thepolychlorides and from 2-chloropropane and recycling it to producepolychlorides, and separating trimethylene chloride from otherpolychlorides produced.

6. The process of producing trimethylene chicride, which consists inchlorinating gaseous propanewith gaseous chlorine to yield monochloridesand polychlorides, separating l-chloropropane from the polychlorides andrecycling it to produce polychlorides, and separating trimethylenechloride from other polychlorides produced.

7. The process of producing trimethylene chloride, which consists inchlorinating gaseous propane with gaseous chlorine to yieldmonochlorides and polychlorides, separating the monochlorides from thepolychlorides and recycling the monochlorides to produce polychloridesand separating trimethylenev chloride from other polychlorides produced.

8. The process of producing trimethylene chloride, which consists inchlorinating gaseous propane with gaseous chlorine to yieldmonochlorides and polychlorides, separating unchlorinated propane andl-chloropropane from the polychlorides and from 2-chloropropane andrecycling said unchlorinated propane and said l-chloropropane tochlorinate them by gaseous chlorine, and separating trimethylenechloride from other polychlorides produced.

9. The process of producing trimethylene chloride, which consists inchlorinating gaseous propane with gaseous chlorine to yieldmonochlorides and polychlorides, separating unchlorinated propane andl-chloropropane from the polychlorides and recycling said unchlorinatedpropane and said l-chloropropane to chlorinate them by gaseous chlorine,and separating trimethylene chloride from other polychlorides produced.

10. The process of producing trimethylene chloride, which consists inchlorinating gaseous propane with gaseous chlorine to yieldmonochlorides and polychlorides, separating unchlorinated propane andthe monochlorides from the polychlorides and recycling saidunchlorinated propane and said monochlorides to chlorinate them bygaseous chlorine, and separating trimethylene chloride from otherpolychlorides produced.

11. The process of chlorinating propane, which consists in separatelypreheating propane and chlorine to a temperature above 250 C., andmixing them in that heated condition to cause them to react, and thenpromptly cooling the products of the reaction.

12. The process of chlorinating propane, which consists in separatelypreheating propane to a temperature above 250 C., and mixing it in thatheated condition with chlorine to cause its chlorination, and thenpromptly cooling the products of the reaction. I

. 13. The process of chlorinating propane, which consists. in separatelypreheating propane and chlorine to a temperature above 250 C., andmixing them in that heated condition to cause them to react, and thenpromptly cooling the products of the reaction; and efl'ecting the mixingof the chlorine with the propane at a velocity above that of flamepropagation under the conditions existing.

14. The process of chlorinating propane, which consists in separatelypreheating propane to a temperature above 250 C., and mixing it in thatheated condition with chlorine to cause its chlorination, and thenpromptly cooling the products of the reaction; and effecting the mixingof the chlorine with the propane at a velocity above that of flamepropagation under the conditions existing.

15. The process of chlorinating propane, which consists in separatelypreheating propane and chlorine to a temperature above 250 C., andmixing them in that heated condition to cause them to react.

16. The process of chlorinating propane, which consists in separatelypreheating propane to a temperature above 250 C., and mixing it in thatheated condition with chlorine to cause its chlorination. I

17. The process of chlorinating l-chloropropane, which consists invaporizing it, mixing it with a hot gaseous diluent so that suchvaporized l-chloropropane will be quickly brought to a desired reactiontemperature, and mixing the mixture of l-chloropropane and heated inertgaseous diluent with preheated chlorine to produce a reaction of thechlorine with the heated l-chloropropane.

18. The process of chlorinating l-chloropro- 20. The process ofchlorinating l-chloropro pane, which consists in mixing it withchlorine, and subjecting the mixture to the action of light. 21. Theprocess of producing trimethylene chloride, which consists in subjectinga gas of the class consisting of propane and l-chloropropane to achlorination reaction with gaseous chlorine under photochemicalconditions which accelerate the reaction, to yield trimethylene chlorideand other chlorides of propane, and separating the trimethylene chloridefrom other chlorides.

22. The process of producing trimethylene chloride, which consists insubjecting a gas of the class consisting of propane and l-chloropropaneto a chlorination reaction with gaseous chlorine under catalyticconditions which accelerate the reaction, to yield trimethylene chlorideand separating and other chlorides of propane,

the trimethylene chloride from other chlorides.

HENRY B. HASS. EARL T. McBEE.

